There's not a lot. Guerrero's works are published in Monumentos de la Musica Espanola, which is still in process, so they haven't gotten to the "dibs and dabs" volume (which, face it, is where the reduced forces music is likely to be.) MBE XIX contains the 3-part works from Cantiones y Villanescas Espirituales, Venice 1589. These are in Spanish, but if you have a Spanish service you could use them, or if you have somebody fluent in Spanish with a gift for words, they could make a singable English version. There's a 3-voice Pange Lingua in a manuscript in Granada, Archivo Manuel de Falla (E-GRmf 975). The Grove dictionary cites a few 2-3 voice works as being intabulated in RISM B I/1 1554-23...which is obviously a misprint, as that's a book of French chansons. RISM 1554-32 is Orphenica lyra, a published anthology of vihuela music, which does contain Guerrero. There's a modern edition pub. Oxford : Clarendon Press, c1978 and a Minkoff facsimile from 1981. You'd have to de-intabulate it by breaking out the parts, stripping out obvious added ornamentation, then adding the words, which is probably more than you want to do, but there's a Fecit potentiam and Susepit Israel in 2 v and Sacris solemnis in 3. Also there are some manuscript motets in Grove w/o voicings given, so there might be more. I haven't scared up any of this online yet...I' ll post if I find anything.